Organic EL displays, which are self-emission type displays, are advantageous in high contrast and high-speed response and are therefore suitable for moving image applications such as televisions which display natural images. In general, organic EL elements are driven by using control elements such as transistors, and multi gray level display may be achieved by driving the transistors with a constant current in accordance with data, or by driving the transistors with a constant voltage to vary the light emission period.
Here, with the constant current driving in which the transistors are used in the saturation region, variations in the characteristics of the transistors such as threshold values and mobility would cause a variation in the electric current flowing in the organic EL element, which results in non-uniform display. In order to deal with this disadvantage, WO 2005/116971 A1 discloses a method in which transistors are used in the linear region and digitally driven with a constant voltage, thereby improving the display non-uniformity.
In the digital driving method disclosed in WO 2005/116971 A1, because one frame period is divided into a plurality of sub frames and each pixel is accessed a number of times corresponding to the number of sub frames, it is necessary to supply data to the data lines at high frequencies in accordance with the sub frames. When the data lines are driven by high frequencies as described above, the power consumption is increased in order to achieve high-speed charge and discharge of the data lines. Further, while a sufficient signal amplitude must be ensured for reliably turning the transistors ON and OFF when there is a variation in the threshold values and the mobility of the transistors, this makes a reduction in the power consumption difficult because the power consumption increases as the amplitude of a signal to be supplied to the data line is increased.